In vivo observations of microcirculation will be made following trauma to brain vessels or the brain itself. In addition to techniques already in the literature a new technique for damaging cerebral vessels will be used, employing light from a mercury lamp and dye as a heat generating target. Platelet aggregation and embolization will be quantified as well as cerebral vasospasm associated with vessel damage and/or platelet aggregation. Vascular reactivity will be tested using agents of potential importance as spasmogens. Drugs will be tested for their capacity to inhibit platelet aggregation at the site of damage and/or for their capacity to prevent vasoconstriction associated with trauma.